Powder coloring system

ABSTRACT

A method for coloring powders is provided that includes mixing a base powder and non-incorporated pigments. A colored powder composition having a base powder particle and at least a partial shell of non-incorporated pigments about the base powder particle is also provided. Articles having a coating of the colored powder composition are also provided.

TECHNICAL FIELD

This invention relates to powder coating compositions and methods fortheir manufacture and use.

BACKGROUND

Powder coatings are an alternative to traditional liquid based coatingsand paints. Liquid based systems are fairly easy to tint and color toproduce a desired color. However, this has not been generally true ofpowder-based systems due to the manufacturing process as well as theapplication process for powders.

Powder coatings are generally manufactured in a multi-step process.Various ingredients, which may include resins, curing agents, pigments,additives, and fillers, are dry-blended to form a premix. This premix isthen fed into an extruder, which uses a combination of heat, pressure,and shear to melt and thoroughly mix the ingredients. As the ingredientsmix together in melted form during the extrusion process, various colorsof pigments can be mixed together to produce a uniform color. Theextrudate is cooled and then ground into a powder. Depending on thedesired coating end use, the grinding conditions are typically adjustedto achieve a powder median particle size of about 25-150 microns.

The final powder may then be applied to an article by various meansincluding the use of fluid beds and spray applicators. Most commonly, anelectrostatic spraying process is used, wherein the particles areelectrostatically charged and sprayed onto an article that has beengrounded so that the powder particles are attracted to and cling to thearticle. After coating, the article is heated. This heating step causesthe powder particles to melt and flow together to coat the article.Optionally, continued or additional heating may be used to cure thecoating. Other alternatives such as UV curing of the coating have beendiscovered and may be used.

A characteristic and limitation of powder coatings that is differentfrom liquid paints is that when powder coatings of two different colorsare blended together, the resultant finish typically has a speckledappearance rather than being uniform in color. For example, if a whitepowder coating is mixed with, or contaminated with, a black powdercoating and then applied, the final coating will have a black and whitespeckled appearance, instead of having a uniform gray color finish.

This characteristic of powder coatings has important implications in theeconomics of powder coatings manufacture, as each powder compositionmust be separated from other powder compositions. However, it isdifficult to quickly and inexpensively change from one powder coatingcomposition color to another. Changing compositions requires completeseparation of product from one batch of colored powder to the next atall stages of manufacturing. At the extruder, this typically requires acomplete purge of the equipment, and then feeding the next compositionuntil it stabilizes. This takes time and results in waste product. Atthe grinder, the entire grinding system must be cleaned. This typicallyrequires major disassembly and cleaning of all grinding equipment andassociated ductwork, and then reassembly, which is a time and laborintensive endeavor. Failure to fully clean the equipment will result inthe second powder color composition having specks of the first colorcomposition in it.

The cleaning process for switching from production of one color toanother is particularly onerous in the production of small batches ofspecial colors. For small batches, it is not uncommon for the cleaningprocess to consume more time and labor than was required to extrude andgrind the batch.

A related problem occurs when a customer requests a custom color powdercoating. If the color initially produced does not match the requestedcolor, then it must be re-fed into the extruder with additional pigmentor material. This requires the whole process, including clean up, to berepeated. Alternatively, the batch may be discarded and an entirely newbatch run to obtain the proper color match.

For all of these reasons, it is difficult, time consuming, and expensiveto produce small amounts of any particular powder coating color. It isgreatly preferred to produce large amounts of the same color, withminimal changeovers. However, due to the overall advantages of powdercoatings, there is a growing acceptance of powder coatings. This is turnhas lead to a greater demand for a wider variety of colors for anincreasing array of applications.

SUMMARY

In one aspect, the invention allows the rapid and cost-effectivecreation of an almost endless variety of powder coating compositions.This is accomplished by enabling the mixing of color onto a powder. Afurther benefit is that this allows different process steps to be runmost efficiently and effectively. Another benefit is that the number ofintermediate materials can be minimized while maximizing the array offinished products available. This provides for an efficientmanufacturing process that minimizes costs associated with inventory andcleanup.

In another aspect, the present disclosure is directed to a methodincluding:

providing at least one base powder having a median particle size of atleast 25 microns;

providing at least one non-incorporated white pigment;

providing at least one non-incorporated coloring pigment; and

mixing the base powder, the non-incorporated white pigment and thenon-incorporated coloring pigment to form a colored mixture, wherein atleast a majority of the non-incorporated white pigments and the coloringpigments on the surface of the base powder are loosely associated withthe base powder and are capable of being re-distributed to another basepowder upon further mixing, and wherein the colored mixture includes atleast 1 wt. % non-incorporated white pigment, based on the total weightof the colored mixture. In a preferred embodiment, the mixture yields afree flowing colored powder.

In yet another aspect, the present disclosure is directed to a method,including:

providing at least one base powder having a median particle size of atleast 25 microns, wherein the base powder is a thermoset material;

providing at least one non-incorporated white pigment;

providing at least one non-incorporated coloring pigment; and

mixing the base powder, the non-incorporated white pigment and thenon-incorporated coloring pigment form a colored mixture, wherein thecolored mixture includes at least 1 wt. % non-incorporated whitepigment, based on the total weight of the colored mixture. In apreferred embodiment, the mixture yields a free flowing colored powder.

In another aspect, the present disclosure is directed to a composition,including:

a base powder particle having a median particle size of at least 25microns; and

at least a partial shell about the base powder particle, wherein theshell includes at least 4,500 non-incorporated white pigment particlesand a plurality of non-incorporated colored pigment particles.

In yet another aspect, an article is provided that has a coating of thepresent invention deposited thereon.

The details of one or more embodiments and aspects of the invention areset forth below. Other features, objects, and advantages of theinvention will be apparent from the description and from the claims.

DETAILED DESCRIPTION

In one embodiment, the present invention provides a method whichincludes the steps of: providing at least one base powder containing upto about 25 wt. % incorporated white pigment; providing at least onenon-incorporated white pigment; providing at least one non-incorporatedcoloring pigment; and mixing the base powder, the white pigment and thecoloring pigment to thereby distribute the non-incorporated pigments andthe base powder to form a colored mixture, wherein the colored mixturecomprises at least about 1 wt. % non-incorporated white pigment. In apreferred embodiment, the mixture yields a free flowing colored powder.

Suitable base powders for use in the present invention preferablyinclude at least one polymeric binder. They may also optionally includeone or more incorporated pigments, opacifying agents or other additives.These ingredients are combined and mixed prior to being fed into anextruder.

Suitable polymeric binders generally include a film forming resin andoptionally a curing agent for the resin. The binder may be selected fromany resin or combination of resins that provides the desired filmproperties. Suitable examples of polymeric binders include thermosetand/or thermoplastic materials, and can be made with epoxy, polyester,polyurethane, polyamide, acrylic, polyvinylchloride, nylon,fluoropolymer, silicone, other resins, or combinations thereof.Thermoset materials are preferred for use as polymeric binders in powdercoating applications, and epoxies, polyesters and acrylics areparticularly preferred. If desired, elastomeric resins may be used forcertain applications.

Examples of preferred binders include the following: carboxyl-functionalpolyester resins cured with epoxide-functional compounds (e.g.,triglycidyl-isocyanurate), carboxyl-functional polyester resins curedwith polymeric epoxy resins, carboxyl-functional polyester resins curedwith hydroxyalkyl amides, hydroxyl-functional polyester resins curedwith blocked isocyanates or uretdiones, epoxy resins cured with amines(e.g., dicyandiamide), epoxy resins cured with phenolic-functionalresins, epoxy resins cured with carboxyl-functional curatives,carboxyl-functional acrylic resins cured with polymeric epoxy resins,hydroxyl-functional acrylic resins cured with blocked isocyanates oruretdiones, unsaturated resins cured through free radical reactions, andsilicone resins used either as the sole binder or in combination withorganic resins. The optional curing reaction may be induced thermally,or by exposure to radiation (e.g., UV, UV-Vis, Visible light, IR, nearIR, and E-beam).

The final base powder may be clear, translucent or opaque. For mostproducts and colors a translucent base powder is preferred. However,clear base powders may be useful for dark colors.

To make a translucent base powder it is preferred to incorporate a whitepigment (e.g., titanium dioxide (TiO₂)) into the powder. As discussedbelow, this may be conveniently accomplished using an extrusion process.The amount of white pigment that is incorporated into the base powder isgenerally less than that required to make a finished colored powderusing the conventional extrusion method. By way of comparison, typicalpowder paints made using the conventional extrusion method containbetween 20 and 35 wt. % white pigment (e.g., TiO₂) dispersed within thepowder. The base powders of the present invention, in contrast,generally contain less than 25 wt. %, more preferably less than 20 wt.%, and most preferably less than 15 wt. % white pigment (e.g., TiO₂)within the base powder. The base powders of the present invention may beclear without any incorporated white pigment (i.e., a clear base powder)but preferably are translucent and incorporate at least 3 wt. %, morepreferably at least 5 wt. %, and most preferably at least 7 wt. % whitepigment (e.g., TiO₂) within the base powder.

As discussed below, additional white pigment (e.g., TiO₂) is mixed withthe base powder, along with one or more coloring pigments. Because thesepigments are not “incorporated” into the base powder, e.g., via anextrusion step, but lie on the surface when the powder is in its freeflowing state (i.e., before the powder is converted into a film), theyare referred to herein as “non-incorporated.” It is recognized that someof the “non-incorporated” pigment may during a subsequent film-formingstep become an intimate part of the composition.

It has been found that the total amount of white pigment (i.e., the sumof the incorporated white pigment within the base powder and thenon-incorporate portion which is distributed on the surface) isapproximately the same amount as is typically used when solely utilizingthe extrusion process to make a finished powder.

The base powder may optionally be colored with dyes or pigments, thoughthis is not preferred in situations where the base powder is to be usedto make a wide variety of final colors. Colored base powders contain asufficient quantity of pigments or dyes to induce some degree of color(and also some opacity), and are useful for colors in which asubstantial portion of the required pigmentation is already included inthe base powder.

The base powder may optionally include other additives. These otheradditives can improve the application of the powder coating, the meltingand/or curing of that coating, or the performance or appearance of thefinal coating. Examples of optional additives which may be useful in thebase powder include: cure catalysts, antioxidants, color stabilizers,slip and mar additives, UV absorbers, hindered amine light stabilizers,photoinitiators, conductivity additives, tribocharging additives,anti-corrosion additives, fillers, texture agents, degassing additives,flow control agents, thixotropes, and edge coverage additives.

The polymeric binder is dry mixed together with any optional additives,and then is typically fed through an extruder. The resulting extrudateis then ground to form a powder. Other methods may also be used. Forexample, one alternative method uses a binder that is soluble in liquidcarbon dioxide. In that method, the dry ingredients are mixed into theliquid carbon dioxide and then sprayed to form the base powderparticles. If desired, powders may be classified or sieved to achieve adesired particle size and/or distribution of particle sizes.

The resulting powder is at a size that can effectively be used by theapplication process. Practically, particles less than 10 microns in sizeare very difficult to apply effectively using conventional electrostaticspraying methods. Consequently, powders having median particle size lessthan about 25 microns are difficult to electrostatically spray becausethose powders typically have a large fraction of small particles.Preferably the grinding is adjusted (or sieving or classifying isperformed) to achieve a powder median particle size of about 25 to 150microns, more preferably 30 to 70 microns, most preferably 30 to 50microns.

The resulting powder preferably has a melt viscosity of at least 90Pa·s, more preferably at least 95 Pa·s, and most preferably at least 100Pa·s, when tested using an ICI cone and plate viscometer set at 160° C.and using a shear rate of 3,600 s⁻¹.

The present invention may also be used to color, or adjust the color of,powders obtained from various suppliers including Valspar, Akzo Nobel,Rohm & Haas, Sherwin Williams and H.B. Fuller.

The base powder optionally contains an incorporated white pigment withinit, and compositions of the present invention contain a non-incorporatedwhite pigment. Suitable white pigments for use as either theincorporated or the non-incorporated white pigments in the presentinvention include any white (or near white) pigment that is capable ofcontributing opacity (i.e., hiding) to the finished composition.Examples of suitable incorporated or non-incorporated white pigmentsinclude titanium dioxide (titanic anhydride, titanic acid anhydride,titanic oxide, titanium white, titania), HITOX (a commercially availableimpure TiO₂ material), powders of zinc sulfide and barium sulphate(e.g., LITHOPONE), aluminum phosphate nanoparticles (e.g., BiPHOR, fromBunge Fertilizantes S. A., Sao Paulo, Brazil), zinc oxide, or otherwhite inorganic pigments. Titanium dioxide is produced, in general by achloride process by which mineral rutile or refined ore is reacted withgaseous chlorine at about 1200° C. in the presence of coke to formliquid titanium tetrachloride. After distillation, the distillate isoxidized in the vapor phase to produce crude pigmentary titaniumdioxide. After treatment, organic and inorganic components may be addedto achieve certain properties.

The median white pigment particle size is suitably about 0.01 to 4.0microns, and preferably about 0.04 to 1.0 microns. Titanium dioxidepigments generally have a median particle size of 0.1 to 0.5 microns,more preferably 0.15 to 0.3 microns.

In addition to any incorporated white pigment within the base powder, asufficient amount of non-incorporated white pigment is mixed with thebase powder, to thereby distribute the non-incorporated pigment (e.g.,on the surface of the base powder). It has been found that the presenceof non-incorporated white pigment in the composition can greatly lessen(or functionally eliminate) the speckled appearance of the final filmformed from the composition. Preferably, at least 1 wt. %, morepreferably at least 2 wt. %, most preferably at least 3 wt. %, andoptimally at least 4 wt. % non-incorporated white pigment is mixed withthe base powder, based on the total dry weight of the powder mixture.While large amounts of non-incorporated white pigment may be mixed withthe base powder, it should be appreciated that too much can adverselyimpact properties such as flow or coalescence. Consequently, preferablythe mixture contains less than about 10 wt. % non-incorporated whitepigment, more preferably less than 8 wt. %, based on the total dryweight of the powder mixture.

Various organic or inorganic coloring pigments may be used in thepresent invention. In dry form, most pigments are highly agglomerated,consisting of clusters of primary particles that are bound together byphysical forces. Suitable coloring pigments include carbon black, rediron oxide, yellow iron oxide, raw umber, phthalocyanine blue,phthalocyanine green, napthol red, toluidine red, various organicyellows, carbazole violet, and quinacridones. If desired, processedcoloring pigments, such as pigments that have been coated with polymericmaterials may be used. Suitable such pigments include SURPASS productsfrom Sun Chemical.

The median pigment particle size is suitably about 0.01 to 4.0 microns,and preferably about 0.04 to 1.0 microns. Organic pigments typicallyhave a median particle size of less than 0.3 microns. Iron oxidepigments typically have a median particle size of 0.2 to 0.6 microns.Carbon black has a median particle size around 0.07 microns, whilephthalocyanine blue typically has a median particle size around 0.05microns.

The amount of non-incorporated coloring pigment mixed onto the basepowder will depend on the desired color of the final product. Theamounts of non-incorporated coloring pigments used in several exemplarycolors are illustrated in the following examples. In general, it hasbeen found that less coloring pigment is needed to produce a particularcolor using the method of the present invention than is needed whenusing conventional extrusion methods (i.e., when all the pigments arecontained within the powder).

Optionally, other additives may be used in the present invention. Asdiscussed above, these optional additives may be added prior toextrusion and be part of the base powder, or may be added postextrusion. Suitable additives for addition after extrusion includematerials that would not perform well if they were added prior toextrusion; materials that would cause additional wear on the extrusionequipment, or other additives. Additionally, optional additives includematerials which are feasible to add during the extrusion process, butwhich are found desirable to add later. The additives may be added aloneor in combination with other additives to provide a desired effect onthe powder finish or the powder composition. These other additives canimprove the application of the powder, the melting and/or curing, or thefinal performance or appearance. Examples of optional additives whichmay be useful include: cure catalysts, antioxidants, color stabilizers,slip and mar additives, UV absorbers, hindered amine light stabilizers,photoinitiators, conductivity additives, tribocharging additives,anti-corrosion additives, fillers, texture agents, degassing additives,flow control agents, thixotropes, and edge coverage additives.

Other preferred additives include performance additives such asrubberizers, friction reducers, and microcapsules. Additionally, theadditive could be an abrasive, a catalyst, heat sensitive, or one thathelps create a porous final coating. Also, additives to improve wettingof the base powder may be added.

Mixing can be carried out by any available mechanical mixer or by manualmixing. Some examples of possible mixers include Henschel mixers(available, for example, from Henschel Mixing Technology, Green Bay,Wis.), Mixaco mixers (available from, for example, Triad Sales, Greer,S.C. or Dr. Herfeld GmbH, Neuenrade, Germany), Marion mixers (availablefrom, for example, Marion Mixers, Inc., 3575 3rd Avenue, Marion, Iowa),invertible mixers, Littleford mixers (from Littleford Day, Inc.),horizontal shaft mixers and ball mills. Preferred mixers would includethose that are most easily cleaned.

The mixing step is preferably performed at a temperature below the glasstransition temperature of the base powder. More preferably, the mixingstep is carried out at a temperature less than 40° C., and even morepreferably at less than 30° C., and under relatively gentle conditions.Typically, the components are stirred together in a suitable mixer for 1to 60 minutes, more preferably 15 to 30 minutes, to provide therequisite mixing. Ideally, regardless of the particular mixing deviceutilized, the mixing time and rpm should be chosen such that there isonly minimal change in particle size. The objective of the mixing stepis to uniformly distribute the base powder particles with the whitepigment and coloring pigment, not to cause significant particle sizechanges. The desired end product is preferably a free-flowing powder.

If desired, the non-incorporated white pigment and the non-incorporatedcoloring pigment may be fused to the base powder or alternatively it maybe weakly associated with the base powder. It is preferred that thenon-incorporated pigments not be fused to the base powder. This enablescolor correction to be made by, for example, adding additional basepowder and “re-distributing” the non-incorporated pigments across allthe base powder present in the mixture. In addition, by not fusing thenon-incorporated pigments to the base powder, unused colored mixturescan be easily blended to form new colors, without the speckledappearance that a blend of fused colored particles might provide. Inpreferred embodiments of the present invention, at least a majority ofthe non-incorporated white and coloring pigments are loosely associatedwith the base powder and are capable of being re-distributed to anotherbase powder upon further mixing. In more preferred embodiments of thepresent invention, at least 75% (and most preferably at least 90%) ofthe non-incorporated white and coloring pigments are loosely associatedwith the base powder and are capable of being re-distributed to anotherbase powder upon further mixing.

One illustrative method of the present invention is to select one ormore base powders, one or more non-incorporated white pigments, and oneor more non-incorporated coloring pigments. The non-incorporatedpigments are added to the base powder(s) by pouring, or any manual,mechanical or automatic means. Other optional additives may be added.This can be poured or added by any manual, mechanical or automaticmeans. These optional additives can be combined with the base powderbefore or after addition of the pigments, or can be premixed with thepigment prior to addition of the pigment. The base powder plus anyadditions are mixed or allowed to become uniformly distributed. Incertain embodiments, the mixing can occur at the same time as anyadditions are made, which may obviate the need for additional orseparate mixing and will provide the required level of uniformity to themixture.

While not wishing to be bound by any theory, presently availableevidence indicates that once the non-incorporated pigments are added tothe base powder, the pigments form a coating layer (in one embodiment apreferably weakly associated layer) on the surface of the base powderparticles. Presently available evidence indicates that the number ofnon-incorporated pigment particles typically associated with each corebase particle varies depending on the size of the base particle, size ofthe pigment/dye particle, and the amount of pigment/dye used. This canbe seen on the following table, which uses a base powder particle sizeof 32 microns in diameter for calculations.

Exemplary Relative pigment usage number Average pigment level (wt % ofof pigment particle diameter, powder particles per Pigment micronscoating) base particle Titanium Dioxide* 0.3 3.5% 15,700 Red Iron Oxide0.2 2.1% 26,000 Yellow Iron Oxide 0.6 2.7% 1,520 Phthalocyanine 0.050.8% 2,110,000 Blue Carbon Black 0.07 0.1% 80,100 Organic Red 0.3 1.2%14,900 *As previously mentioned, additional TiO₂ may be incorporatedinto the base powder. This calculation only accounts for thenon-incorporated TiO₂, not any TiO₂ that may be within the base powder.

In one embodiment, the present invention provides a powder coatingcomposition that comprises a plurality of powder particles, wherein thepowder particles have at least a partial shell of non-incorporated whiteand coloring pigment particles. Preferred such compositions comprise abase powder particle having a median particle size of 25 to 150 microns,more preferably 30 to 70 microns, most preferably 30 to 50 microns.Preferred such compositions comprise at least 4,500 non-incorporatedTiO₂ particles, more preferably at least 9,000 non-incorporated TiO₂particles associated with or on the surface thereof.

In one embodiment a colored mixture is prepared by mixing at least onebase powder, at least one non-incorporated white pigment, and at leastone non-incorporated coloring pigment, to thereby distribute thenon-incorporated pigments and the base powder. A sample of the coloredmixture can then be assessed (e.g., applied to a substrate and comparedto a target color or target color value) to ensure that the desiredcolor has been achieved. If the color is not within specification, thenadditional quantities of base powder, non-incorporated white pigment,and/or non-incorporated coloring pigment may be added to the initialcolored mixture and mixed. The second mixing step preferablyredistributes the non-incorporated pigments and the base powders to forman adjusted colored mixture having the desired color.

In another embodiment, traditionally prepared powder paints (e.g., apowder paint formed using the extrusion method) may be tinted using themethod of the present invention. Namely, the powder paint is tinted to adifferent color (or different shade) by mixing the powder paint with atleast one non-incorporated white pigment and at least onenon-incorporated coloring pigment, to thereby distribute thenon-incorporated pigments and the powder paint and change the color ofthe powder paint.

The completed powder of the present invention may be applied to asubstrate using any conventional method, including spraying,electrostatic spraying, fluidized beds and the like. Following powderapplication, the substrate is heated to a temperature sufficient tocause the powder particles to melt and flow. Various heating sources maybe used, including convection heating, infrared heating, near-infraredheating, induction heating, or a combination thereof. Optionally, thepowder may be applied to a preheated substrate.

Then the coating is optionally cured, and such curing may occur viacontinued heating, subsequent heating, or residual heat in thesubstrate. In another embodiment of the invention, if a radiationcurable powder coating base is selected, the powder can be melted by arelatively short or low temperature heating cycle, and then may beexposed to radiation to initiate the curing process. One example of thisembodiment is a UV-curable powder. Other examples of radiation curinginclude using UV-Vis, Visible light, near-IR, IR and E-beam.

Preferably, the coated substrate is uniformly colored and has thedesirable physical and mechanical properties. By “uniformly colored” ismeant that a coated substrate appears unspeckled (or only minimallyspeckled) to the naked eye at a distance of approximately 0.3 meters.More preferably, the coated substrate is uniformly colored when examinedat this distance under 2× magnification. Thickness of the final filmcoating depends upon the desired application of the substrate and theadditives selected. Typically, the final film coating will have athickness of 25 to 200 microns.

Another feature of the current invention is that less coloring pigmentmay be needed to produce the same color in the final film coating. Thismay vary depending on the pigment used, but typically about 25% lesscoloring pigment is required than if the coloring pigment is mixedthoroughly with the film forming resin, such as occurs in the extruder.Additionally, in the current invention, some white pigment and somecoloring pigment is at the surface of the particles, rather than beingthroughout the powder particles. This allows the same amount of pigmentat the surface of the final film coating with less pigment being added.Illustratively, when one makes a very thin cut through the final filmcoating and examines the exposed cut under a microscope, the pigmentappears to be distributed at the interface of the coalesced base powder.

It was a surprising finding that for powders of the present inventionthat have non-incorporated coloring pigment, there should also be atleast a portion of the white pigment that is non-incorporated.

While not intending to be bound by theory, Applicants believe that thisfinding can be explained when one considers the three-dimensionalgeometry of the coated powders and the two-dimensional appearance offilms of these particles.

Notably, assuming that the non-incorporated white pigment and coloringpigments are fairly uniformly distributed on the surface of the basepowder, the pigments will not appear to be uniformly distributed. Forpurposes of this illustration, the base powder may be roughlyapproximated as a sphere. As such, the pigments form a shell or partialshell on the surface of the powder. When an observer views a film ofthese powders, the spheres will have coalesced and appear in projectionas a hexagon. The pigment that is lying on top of the center of thehexagon will appear less intense (as it is only one layer thick) thanpigment that is on the “edges” of the hexagon. This is because the“edge” of the hexagon is actually a view down the side of thethree-dimensional particle and the eye sees a thicker cross-section ofpigment.

Applicants have surprisingly found that when no non-incorporated whitepigment is mixed with the base powder, the non-incorporated coloringpigments provide a “speckled” appearance. When a sufficient amount ofthe non-incorporated white pigment is mixed with the base powder andcoloring pigments the final film appearance is more uniform. Thisuniformity cannot be achieved simply by incorporating the white pigmentin the base powder. Doing so will perhaps make the overall film moreopaque, but the appearance of the color will still be speckled as thepigment will still appear concentrated at the interface of adjoiningpowders.

The following examples are offered to aid in understanding of thepresent invention and are not to be construed as limiting the scopethereof. Unless otherwise indicated, all parts and percentages are byweight.

EXAMPLES

Several materials cited in the following examples were evaluated bytests common in the industry. These test results were obtained frommanufacturer literature. Acid value measures milligrams of potassiumhydroxide reacted per gram of resin.

The following are raw material suppliers for various ingredients listedin the examples below. Crylcoat 630 and Crylcoat 440 are products ofCytec Surface Specialties. PF-67 is a product of Estron. R-960 and R-900are products of DuPont. Raven 450 is a product of Columbian Carbon. YZ1688 and R 2899 are products of Elementis. Crematt 8600 is a product ofBayer.

The following “Uniformity Rating Scale” is used in the Examples.

-   -   1 Very speckled; speckles easily visible at a distance of 0.6 m.    -   2 Very speckled; speckles visible at a distance of 0.6 m.    -   3 Very speckled; speckles easily visible at a distance of 0.3 m.    -   4 Moderately speckled; speckles visible at a distance of 0.3 m.    -   5 Slightly speckled; speckles visible at a distance of 0.3 m.    -   6 Very slightly speckled; speckles visible at a distance of 0.3        m.    -   7 Very slightly speckled; speckles visible only upon careful        examination at a distance of 0.3 m.    -   8 Uniformly colored; no speckles visible to the unaided eye,        easily visible speckles with 2× magnification.    -   9 Uniformly colored; no speckles visible to the unaided eye,        slightly visible speckles with 2× magnification.    -   10 Uniformly colored; no speckles visible to the unaided eye or        with 2× magnification.        Under the above rating scale, it is believed that uniformity        ratings of 6 or above should be commercially acceptable for many        powder coatings applications, and that ratings of 8 or above        should be acceptable for almost all customers and end-uses.

Example 1 Preparation of White Polyester Powder Coating Base

TABLE 1 Ingredient Parts by weight Polyester Resin (Crylcoat 630, Acidvalue 30-36) 823.0 Polyester Resin (Crylcoat 440, Acid value 32-38)823.0 Triglycidylisocyanurate Curing Agent 124.0 Acrylic Flow ControlAgent (PF-67) 20.0 Benzoin 10.0 Titanium Dioxide (R-960) 200.0 Total2000.0

The above ingredients were dry blended, then extruded. The extrudate wascooled, combined with 0.2% of Degussa Aluminum Oxide C dry flow agent,and then ground on an air classifying mill to a median particle size of33.0 microns, as determined by a Malvern Mastersizer 2000 laser particlesize analyzer. The resulting white polyester powder coating base wasused for subsequent blending studies as described below.

Example 2 Preparation of Gray Polyester Powder Coatings

TABLE 2 2A 2B Ingredient (parts by weight) (parts by weight) Whitepolyester powder coating 1200.0 1200.0 base (Example 1) Titanium Dioxide(R-960) — 90.0 Carbon Black (Raven 450) 3.0 3.0

The ingredients shown in Table 2 were mixed in a laboratory Reos Mixer,which consists of a vertical shaft driving an agitator blade suspendedin the mixing chamber, and revolving at a speed of 1725 rpm. The mixingtime used for both samples was 8 minutes. The resulting products wereboth free flowing powders, which did not visually appear to containsignificant quantities of agglomerates or oversize particles. Bothsamples were successfully electrostatic sprayed without sieving, thenbaked for 20 minutes at 190° C. The cured film from sample 2A showed anon-uniform or speckled appearance with the naked eye, while the filmfrom sample 2B was much more uniform, with only a very slight trace ofspeckling that could be discerned with the unaided eye. Using theuniformity rating scale above, sample 2A was rated a 1, and sample 2Bwas rated a 7. In addition, the film from sample 2A produced anoticeable edge framing effect, with the edges of the coated panel beingnoticeably darker than the center of the panel. Sample 2B produced nonoticeable edge framing effect.

Example 3 Preparation of Tan Polyester Powder Coating

TABLE 3A Ingredient Parts by weight White Polyester Powder Coating Base11804 (Example 1) Titanium Dioxide (R-960) 1132 Yellow Iron Oxide (YZ1688) 41.5 Red Iron Oxide (R2899) 19.8 Carbon Black (Raven 450) 5.8Total 13003.1

The ingredients listed in Table 3A were combined in a Littleford mixerModel FM-50D, equipped with a cooling jacket. The contents were mixedusing both plow agitator and chopper blade at a product temperature of27° C., for a mixing time of 20 minutes. The product was discharged fromthe mixer and sieved through a 94T-mesh screen.

Particle size analysis of the final product showed it to have a medianparticle size of 33.0 microns. Further comparison of the particle sizedistribution data from this sample versus the starting material whitebase from Example 1 showed that although the median particle size of thetwo samples were identical to within the nearest 0.1 micron, the samplefrom example 3 showed traces of a bi-modal distribution, with thesmaller peak centered at about 0.8 microns and distributed between about0.2 microns and 2.2 microns. The overall distribution showedapproximately 3.5% between 0.2 micron and 2.2 microns. The startingmaterial, white base from example 1, on the other hand, showed noevidence of bi-modal

distribution, and had less than 1.0% below 2.2 microns. The top-sizes ofboth samples were very similar, showing traces at 105 microns, butnothing above 120 microns.

After spraying a sample of Example 3 and curing for 20 minutes at 190°C., the resulting cured film gave gloss readings of 85 (60 degreegeometry) and 66 (20 degree geometry). Smoothness of the cured film wasrated as being similar to the color standard that had been previouslyproduced from powders made by the conventional extrusion process. Thecolor uniformity of the cured film was rated as being totally uniform tothe naked eye, and only traces of speckles were visible when evaluatedwith the aid of a 2× magnifier. Using the uniformity rating scale above,sample 3A was rated a 9.

For reference and comparison purposes, the color pigment compositionused in Table 3A is shown in Table 3B below (given in weight-%, based onboth pigment and on total formula), along with the color pigmentcomposition used to commercially produce this same color using theconventional process of extruding all ingredients together (includingcolored pigments), followed by grinding to a finished powder.

TABLE 3B Conventional Process Invention (on (on Ingredient pigment) (ontotal) pigment) (on total) Titanium Dioxide 93.37 15.9 49.56 9.06(Incorporated) Titanium Dioxide (Non- 0 0 47.62 8.71 Incorporated)Yellow Iron Oxide 4.58 0.8 1.74 0.32 Red Iron Oxide 1.69 0.3 0.83 0.15Carbon Black 0.36 0.1 0.24 0.04 Total 100 17.1 99.99 18.28

Example 4 Preparation of Buff Yellow Polyester Powder Coating

TABLE 4A Ingredient Parts by weight White Polyester Powder Coating Base14301 (Example 1) Titanium Dioxide (R-960) 1742.1 Yellow Iron Oxide (YZ1688) 196.5 Red Iron Oxide (R2899) 9.3 Carbon Black (Raven 450) 2.6Total 16251.5

The ingredients listed in Table 4A were mixed in a Littleford FM-50D,using the plows and chopper blade for 20 minutes, at a jackettemperature of 21-22° C., and a product temperature of 21-23° C. Theproduct was discharged and sieved through a 94T-mesh screen. The medianparticle size was found to be 31.4 microns, and a bi-modal distributionwas evident, with 4.5% found between 0.2 microns and 2.2 microns. Thetop-size was 105 microns. A sample was electrostatic sprayed and bakedfor 20 minutes at 190° C. Gloss readings for the cured film were 86/63(60 degree/20 degree geometry). Visual comparison of the cured filmversus the same color produced by conventional extrusion and millingtechniques indicated that the two samples were comparable in smoothness.Color uniformity was rated as totally uniform to the naked eye, and onlyslight traces of speckles were visible under 2× magnification. The curedfilm was rated 9 according to the uniformity rating scale above.

Table 4B shows the pigment composition used to prepare this example,expressed as percent by weight on pigment and on total formula, versusthe commercial formula used to prepare the same color by theconventional extrusion process.

TABLE 4B Conventional Process Invention (on (on Ingredient pigment) (ontotal) pigment) (on total) Titanium Dioxide 86.45 16.27 44.19 8.78(Incorporated) Titanium Dioxide (Non- 0 0 49.36 9.81 Incorporated)Yellow Iron Oxide 13.01 2.45 6.08 1.21 Red Iron Oxide 0.42 0.08 0.290.06 Carbon Black 0.12 0.02 0.08 0.02 Total 100 18.82 99.99 19.88

Example 5 Preparation of Dark Tan Polyester Powder Coating

TABLE 5A Ingredient Parts by weight White Polyester Powder Coating 16690Base (Example 1) Titanium Dioxide (R-960) 989.4 Yellow Iron Oxide (YZ1688) 90.8 Red Iron Oxide (R2899) 4.5 Carbon Black (Raven 450) 12.6Total 17787.3

The ingredients listed in Table 5A were mixed in a Littleford FM-50D for20 minutes, with plows and chopper mixing. A jacket temperature of 21°C. was maintained, and the product temperature was 23° C. during themixing cycle. The product was discharged and sieved through a 105-Tscreen. The median particle size of the product was found to be 33.4microns, with a bi-modal distribution evident, and 2.4% found between0.3 and 2.2 microns. A sample was sprayed and cured for 20 minutes at190° C. The cured film gave gloss readings of 89 (60 degree geometry)and 63 (20 degree geometry). The color appeared visually uniform to the

unaided eye. Under 2× magnification, slight traces of speckles and avery slight degree of darkening at the edges of the panel were visible.The uniformity rating using the previously described scale was 7.

Table 5B shows the pigment composition used to prepare this example,expressed as percent by weight on pigment and on total formula, versusthe commercial formula used to prepare the same color by theconventional extrusion process.

TABLE 5B Conventional Process Invention (on (on Ingredient pigment) (ontotal) pigment) (on total) Titanium Dioxide 90.69 15.38 60.29 9.36(Incorporated) Titanium Dioxide (Non- 0 0 35.81 5.56 Incorporated)Yellow Iron Oxide 8.36 1.42 3.29 0.51 Red Iron Oxide 0.29 0.05 0.16 0.03Carbon Black 0.66 0.11 0.46 0.07 Total 100 16.96 100.01 15.53

Example 6 Semi-Gloss White Hybrid Powder Coating Base

TABLE 6 Ingredient Parts by weight Polyester Resin (Acid number 35) 1082Solid Epoxy Resin 648.3 Matting agent (Crematt 8600) 39.6 TitaniumDioxide (R-960) 200 Acrylic flow control agent (PF-67) 20 Benzoin 10Total 1999.9

The ingredients of Table 6 were dry blended, then extruded. Theextrudate was cooled, combined with 0.2% of Degussa Aluminum Oxide C dryflow agent, and then ground on an air classifier mill to a medianparticle size of 33.9 microns. The sample showed less than 0.2% below2.2 microns, and a top-size of 120 microns. The resulting semi-glosswhite hybrid powder coating base was used in further blending studies asdescribed below.

Example 7 Re-Distribution of Non-Incorporated Pigment

TABLE 7A Ingredient Parts by weight Semi-gloss White Hybrid Powder 9080Coating Base (Example 6) Titanium Dioxide (R-900) 700 Yellow Iron Oxide(YZ 1688) 20 Red Iron Oxide (R2899) 15 Carbon Black (Raven 450) 40 Total9855

The ingredients listed in Table 7A were charged to a Littleford FM-50D.The contents were mixed with plows and chopper for 20 minutes using ajacket temperature set-point of 21° C., and a product temperature of25-26° C. A sample (identified as sample 7-1) was withdrawn and sprayed,yielding a uniform gray appearance.

An additional 4540 parts of white base were then added to the mixer, andthe contents were mixed for five seconds using the plows only, withoutrunning the chopper. A sample (sample 7-2) was withdrawn and sprayed,producing a noticeably speckled appearance. Mixing was continued withthe plows for an additional five minutes, and then another sample waswithdrawn and sprayed, still producing a noticeably speckled appearance.This process was repeated, using the mixing times (with plows only, nochopper) shown in Table 7B. Finally, both plows and chopper were run foran additional mixing cycle of 20 minutes duration (Sample 7-7). Theappearance ratings shown in Table 7B are the numeric average of ratingsgiven by three independent observers, rounded to the nearest wholenumber.

TABLE 7B Mixing time (cumulative) after Sample number White baseaddition Rating 7-1 Before white base addition 8 7-2 5 seconds 2 7-3 5minutes 3 7-4 20 minutes 4 7-5 1 hour 5 7-6 2 hours 4 7-7 3 hours 6 7-83 hours + 20 minutes chopper 6

Example 8 Comparative Blending of Black and White Finished Powders inAbsence of Non-Incorporated Pigment

The following comparative example used the general mixing technique ofExample 7, but all of the pigments were incorporated by extrusion intotheir respective base powders. 11350.0 parts by weight of the whitepolyester powder coating base described in Example 1 were charged to aLittleford FM-50D, and 2270.0 parts of a commercial black finishedpowder coating (Valspar product code 116B) were added. The contents weremixed for the same times and mixing conditions shown in Table 7B.Samples were withdrawn at selected intervals, sprayed, baked for 15minutes at 190° C., and rated for visual uniformity in Table 8.

TABLE 8 Mixing time (cumulative) after Sample number White base additionRating 8-1 5 seconds 1 8-2 5 minutes 1 8-3 20 minutes 1 8-4 1 hour 1 8-52 hours 1 8-6 3 hours 1 8-7 3 hours + 20 minutes chopper 1

In contrast to the improvement in uniformity with mixing time that wasobserved for Example 7, cured films produced from the samples of Example8 (Comparative) showed no discernable improvement in color uniformitywith increased mixing time. All of the samples of Example 8 producedfilms that were very non-uniform and highly speckled. When rated bythree different observers, samples 8-1 and 8-7 were rated as being equalin appearance to each other.

Example 9 Comparative Blending of Black and White Powders withNon-Incorporated White Pigment

The final product produced in Example 8 (approximately 13000 parts byweight) was re-loaded into the Littleford FM-50D, and 1050.0 parts ofR-900 Titanium Dioxide was added. The contents were mixed for 20 minuteswith both plows and chopper, using a jacket temperature of 21° C. Theproduct was then discharged, and a sample was sprayed and cured 20°-190°C. The resulting cured film was highly speckled in appearance, similarto the films produced from Example 8, and was rated a 1 for uniformityaccording to the previously described uniformity rating scale.

Example 10 Preparation of Clear Semi-Gloss Hybrid Powder Coating Base

TABLE 10 Ingredient Parts by weight Polyester Resin (Acid number 35)1623 Solid Epoxy Resin 972.5 Matting agent (Crematt 8600) 59.4 Acrylicflow control agent (PF-67) 30 Benzoin 15 Total 2699.9

The ingredients shown in Table 10 were dry blended, then extruded. Theextrudate was cooled, combined with 0.2% of Degussa Aluminum Oxide C dryflow agent, and then ground on an air classifier mill to a medianparticle size of 34.1 microns. The resulting semi-gloss clear hybridbase was used in further blending studies as described below.

Example 11 Preparation of Semi-Gloss Dark Gray Hybrid Powder Coating

TABLE 11A Ingredient Parts by weight Clear Semi-gloss Hybrid Powder11350 Coating Base (Example 10) Titanium dioxide (R-900) 715.5 YellowIron Oxide (YZ 1688) 21.1 Red Iron Oxide (R 2899) 18.2 Carbon Black(Raven 450) 50.8 Total 12155.6

The ingredients listed in Table 11A were mixed in a Littleford modelFM-50D using a jacket temperature set-point of 18° C., for 30 minutes,with both plows and chopper. During this mixing cycle, the producttemperature dropped from 27° C. initial temperature to 23° C. finaltemperature. A sample was withdrawn and sprayed (Sample 11-1). Mixingwas then continued for an additional 30 minutes, this time increasingthe jacket temperature set-point to 41° C. The product temperatureduring this second mixing cycle was 25° C. initial, and increasedgradually to a 40° C. final temperature. A sample was withdrawn andsprayed (Sample 11-2). Comparison of the two spray-outs from samples11-1 and 11-2 indicated that the color, uniformity, and generalappearance of the two were equal. Because the color of these samples didnot match the desired color standard sufficiently closely, incrementaladditions of additional pigments and base were made, using mixing cyclesof 20 to 30 minutes after each addition, at a jacket temperatureset-point of 21a C, until a satisfactory color match was achieved. Thefinal composition of the mixture after all additions is shown in Table11B. Cured films obtained from the final product gave a 60 degree glossreading of 62 and an appearance rating of 10. The median particle sizeof the final product was 35.3 microns.

TABLE 11B Ingredient Parts by weight Clear Semi-gloss Hybrid Powder13620 Coating Base (Example 10) Titanium dioxide (R-900) 1315.5 YellowIron Oxide (YZ 1688) 66.1 Red Iron Oxide (R 2899) 28.2 Carbon Black(Raven 450) 53.8 Total 15083.6

Table 11C shows the final pigment composition used to prepare thisexample, expressed as percent by weight on pigment and on total formula,versus the commercial formula used to prepare the same color by theconventional extrusion process.

TABLE 11C Conventional Process Invention (on (on Ingredient pigment) (ontotal) pigment) (on total) Titanium Dioxide 88.82 6.56 0 0(Incorporated) Titanium Dioxide (Non- 0 0 89.88 8.72 Incorporated)Yellow Iron Oxide 2.61 0.19 4.52 0.44 Red Iron Oxide 2.25 0.17 1.93 0.19Carbon Black 6.31 0.47 3.68 0.36 Total 99.99 7.39 100.01 9.71

Example 12 Preparation of Semi-Gloss Beige Hybrid Powder Coating

TABLE 12A Ingredient Parts by weight Semi-gloss White Hybrid Powder12150 Coating Base (Example 6) Titanium dioxide (R-900) 1416 Yellow IronOxide (YZ 1688) 45.9 Red Iron Oxide (R 2899) 3.4 Carbon Black (Raven450) 2.7 Total 13618

The ingredients listed in Table 12A were combined in a Littleford modelFM-SOD mixer with both plows and chopper for 30 minutes, using a jacketset-point of 49° C. Under these mixing conditions, with an initialproduct temperature of 26° C., at the end of the 30 minute mixing cycle,the product temperature had reached a peak of 46° C. A sample of theresulting product was sprayed and baked for 20 minutes at 190° C. Thecured film had a 60 degree gloss of 63, and was rated a 9 foruniformity. The median particle size was found to be 34.6 microns, with2.2% found below 2.2 microns, and a top-size of 120 microns.

Table 12B shows the pigment composition used to prepare this example,expressed as percent by weight on pigment and on total formula, versusthe commercial formula used to prepare the same color by theconventional extrusion process.

TABLE 12B Conventional Process Invention (on (on Ingredient pigment) (ontotal) pigment) (on total) Titanium Dioxide 96.57 33.09 45.24 8.90(Incorporated) Titanium Dioxide (Non- 0 0 52.82 10.40 Incorporated)Yellow Iron Oxide 3.25 1.11 1.71 0.34 Red Iron Oxide 0.06 0.02 0.13 0.02Carbon Black 0.13 0.04 0.10 0.02 Total 100.01 34.26 100 19.68

Example 13 Preparation of Gray Powder Coating by Ball Milling in aDisposable Container

A plastic container 125 mm in diameter and 100 mm tall was filledapproximately 25% full of 17 mm diameter solid glass spheres. 150 partsby weight of the white semi-gloss hybrid powder coating base describedin Example 6 were added, followed by 11.5 parts by weight of R-900titanium dioxide and 0.66 parts by weight of Raven 450 carbon black. Thecontainer was fitted with a lid, and then was rolled for 13.5 hours. Asample of the resulting powder was withdrawn, sprayed, and baked for 20minutes at 190° C. The cured film gave a uniformity rating of 7.

Having thus described the preferred embodiments of the presentinvention, those of skill in the art will readily appreciate that theteachings found herein may be applied to yet other embodiments withinthe scope of the claims hereto attached. The complete disclosure of allpatents, patent documents, and publications are incorporated herein byreference as if individually incorporated.

What is claimed is:
 1. A method, comprising: providing at least one basepowder having a median particle size of at least 25 μm; providing atleast one non-incorporated white pigment; providing at least onenon-incorporated coloring pigment; and mixing the base powder, thenon-incorporated white pigment and the non-incorporated coloring pigmentin dry form for about 15 to 30 minutes to form a colored mixture,wherein at least a majority of the non-incorporated white pigments andthe coloring pigments on the surface of the base powder are distributedon the surface of the base powder and are capable of beingre-distributed to another base powder upon further mixing, wherein thecolored mixture is a free flowing powder, and wherein the coloredmixture comprises at least 1 wt. % non-incorporated white pigment, basedon the total weight of the colored mixture.
 2. The method of claim 1,wherein the base powder comprises up to 25 wt. % of an incorporatedwhite pigment, based on the total weight of the base powder.
 3. Themethod of claim 1, wherein the mixing step is accomplished at atemperature below 40° C.
 4. The method of claim 1, wherein the mixingstep does not cause significant change in the particle size of the basepowder.
 5. The method of claim 1, wherein the base powder has a medianparticle size of 30 to 70 μm and a melt viscosity of at least 90 Pas at160° C.
 6. The method of claim 1, wherein the base powder is notcolored.
 7. The method of claim 1, wherein the base powder is colored.8. The method of claim 1, wherein the method further comprises the stepsof: measuring the color of a sample of the colored mixture of claim 1;adding additional quantities of base powder, non-incorporated whitepigment, and/or non-incorporated coloring pigment to the coloredmixture; and mixing the colored mixture and additional quantities ofbase powder, non-incorporated white pigment, and/or non-incorporatedcoloring pigment to redistribute the non-incorporated pigments acrossthe base powders to form an adjusted colored mixture having a differentcolor.
 9. A method, comprising: providing at least one base powderhaving a median particle size of at least 25 μm, wherein the base powderis a thermoset material; providing at least one non-incorporated whitepigment; providing at least one non-incorporated coloring pigment; andmixing the base powder, the non-incorporated white pigment and thenon-incorporated coloring pigment in dry form for about 15 to 30 minutesto form a colored mixture, wherein the colored mixture comprises atleast 1 wt. % non-incorporated white pigment, based on the total weightof the colored mixture, and wherein the colored mixture is afree-flowing powder.
 10. The method of claim 9, wherein the base powdercomprises up to 25 wt. % of an incorporated white pigment, based on thetotal weight of the base powder.
 11. The method of claim 9, wherein thecolored mixture comprises at least 2 wt. % non-incorporated whitepigment, based on the total weight of the colored mixture.
 12. Themethod of claim 9, wherein the colored mixture comprises at least 3 wt.% non-incorporated white pigment, based on the total weight of thecolored mixture.
 13. The method of claim 9, wherein the base powdercontains between 3 and 15 wt. % of an incorporated white pigment, basedon the total weight of the base powder, and the colored mixturecomprises between 2 and 10 wt. % non-incorporated white pigment, basedon the total weight of the colored mixture.
 14. The method of claim 9,wherein base powder comprises between 7 and 15 wt. % of an incorporatedTiO₂, based on the total weight of the base powder, and the coloredmixture comprises between 4 and 8 wt. % non-incorporated TiO₂, based onthe total weight of the colored mixture.
 15. The method of claim 14,wherein the white pigment is selected from the group consisting oftitanium dioxide, HALOX, powders of zinc sulfide and barium sulphate,aluminum phosphate nanoparticles, and zinc oxide.
 16. The method ofclaim 9, wherein the colored mixture is a free flowing powder.
 17. Themethod of claim 8, wherein at least a majority of additional quantitiesof the non-incorporated white pigments and the non-incorporated coloringpigments on the surface of the base powder are distributed on thesurface of the base powder and are capable of being redistributed toanother base powder upon further mixing.